<template>
  <div class="progress-bar" ref="progressBar" @click="progressClick">
    <div class="bar-inner">
      <div class="progress" ref="progress"></div>
      <div
        class="progress-btn-wrapper"
        ref="progressBtn"
        @touchstart.prevent="progressTouchStart"
        @touchmove.prevent="progressTouchMove"
        @touchend="progressTouchEnd"
      >
        <div class="progress-btn"></div>
      </div>
    </div>
  </div>
</template>

<script>
import { prefixStyle } from 'common/js/dom';
const transform = prefixStyle('transform');
// 小球的宽度
const progressBtnWidth = 16;

export default {
  props: {
    value: { type: Number, default: 0 },
  },
  data() {
    return {
      touch: { initiated: false },
    };
  },
  watch: {
    value(newValue) {
      // 没有在拖动的时候
      if (newValue >= 0 && !this.touch.initiated) {
        const barWidth = this.$refs.progressBar.clientWidth - progressBtnWidth;
        // 根据传入的百分比 计算 offsetWidth
        const offsetWidth = newValue * barWidth;
        this._offset(offsetWidth);
      }
    },
  },
  methods: {
    _offset(offsetWidth) {
      this.$refs.progress.style.width = `${offsetWidth}px`;
      this.$refs.progressBtn.style[transform] = `translate3d(${offsetWidth}px,0,0)`;
    },
    progressTouchStart(e) {
      this.touch.initiated = true;
      this.touch.startX = e.touches[0].pageX;
      this.touch.left = this.$refs.progress.clientWidth;
    },
    progressTouchMove(e) {
      if (!this.touch.initiated) {
        return;
      }
      const deltaX = e.touches[0].pageX - this.touch.startX;
      const offsetWidth = Math.min(
        this.$refs.progressBar.clientWidth - progressBtnWidth,
        Math.max(0, this.touch.left + deltaX)
      );
      this._offset(offsetWidth);
    },
    progressTouchEnd() {
      this.touch.initiated = false;
      this._triggerPercent();
    },
    progressClick(e) {
      const rect = this.$refs.progressBar.getBoundingClientRect();
      const offsetWidth = e.pageX - rect.left;
      this._offset(offsetWidth);
      // 这里当我们点击 progressBtn 的时候，e.offsetX 获取不对
      // this._offset(e.offsetX)
      this._triggerPercent();
    },
    _triggerPercent() {
      const barWidth = this.$refs.progressBar.clientWidth - progressBtnWidth;
      const percent = this.$refs.progress.clientWidth / barWidth;
      this.$emit('input', percent);
    },
  },
};
</script>

<style scoped lang="stylus">
@import "~common/stylus/variable"

.progress-bar
  height: 30px
  .bar-inner
    position: relative
    top: 13px
    height: 4px
    background: rgba(0, 0, 0, 0.3)
    .progress
      position: absolute
      height: 100%
      background: $color-theme
    .progress-btn-wrapper
      position: absolute
      left: -8px
      top: -13px
      width: 30px
      height: 30px
      &.click
        animation: myScale 0.2s;
      .progress-btn
        position: relative
        top: 7px
        left: 7px
        box-sizing: border-box
        width: 16px
        height: 16px
        border: 3px solid $color-text
        border-radius: 50%
        background: $color-theme

@keyframes myScale
  0%
    transform: scale(1)
  80%
    transform: scale(1.3)
  100%
    transform: scale(1.2)
</style>
